Network management system, network management computer and network management method

ABSTRACT

A network management system comprising: a network including a plurality of packet relay apparatuses; wherein the plurality of packet relay apparatuses include first packet relay apparatuses, second packet relay apparatuses, and third packet relay apparatuses located downstream of the first packet relay apparatuses and the second packet relay apparatuses, wherein each of the third packet relay apparatuses has a first path coupled to one of the first packet relay apparatuses to send and receive traffic and a second path coupled to one of the second packet relay apparatuses and being in a blocking state, a management computer includes: a state information collection unit for acquiring state information on the first to the third packet relay apparatuses; and a power management unit for selecting a candidate packet relay apparatus to be deactivated satisfying predetermined conditions based on the state information.

CLAIM OF PRIORITY

The present application claims priority from Japanese patent applicationJP 2012-176358 filed on Aug. 8, 2012, the content of which is herebyincorporated by reference into this application.

BACKGROUND

This invention relates to a management system, a management computer,and a management method for a network including a plurality of packetrelay apparatuses.

To provide cloud services, a data center includes a large number ofcomputers, storage apparatuses and packet relay apparatuses installedtherein. In general, networks composed of a large number of packet relayapparatuses in data centers are trending toward large scale Layer 2networks. The Layer 2 network is a system that transfers packets inaccordance with destination MAC addresses of the packets; the packetsare reachable to all of the packet relay apparatuses in the network.Because of this feature, careless coupling of packet relay apparatuseswith Ethernet cables might cause a problem that a loop is created inwhich packets circulate around the loop to be amplified. To prevent thisproblem, the Layer 2 network usually uses STP (Spanning Tree Protocol).According to the STP, protocol packets are exchanged between packetrelay apparatuses to determine a packet relay apparatus for a root nodefrom a plurality of packet relay apparatuses to create a tree networkwith the root node at the top. Packets can be transmitted only throughthe paths forming the tree and cannot be transmitted through the otherpaths in a blocking state.

In the meanwhile, a network in a data center includes a large number ofpacket relay apparatuses installed therein and also requires a largenumber of cooling devices to cool the heat generated by the packet relayapparatuses. For this reason, the network in a data center tends toconsume a huge electric power. Currently, to lower the power consumptionin a packet relay apparatus, technology for power saving is beingactively developed. For example, according to JP 2010448023 A, edgerouters measure the traffic volume in the network and if the trafficvolume is smaller than the capacity of a first core router, a secondcore router is shifted to a power saving mode and the edge routersupdate the routing table to transfer packets for the second core routerto the first core router.

SUMMARY

The power saving technology focusing on a single packet relay apparatuslike the above-described JP 2010-148023 A, however, might be difficultin handling in practical use because of effect on the traffic flowing inthe network. In the case of JP 2010-148023 A, when a packet relayapparatus is suddenly changed into a power saving mode and the packetthroughput is lowered, packets transferred to the alternate packet relayapparatus might be lost without being processed at the alternate packetrelay apparatus.

An object of this invention is to provide a network management systemand a network management terminal that can reduce the power consumptionin the network without serious effect on the traffic flowing in thenetwork in the data center.

A representative aspect of this invention is as follows. A networkmanagement system comprising: a network including a plurality of packetrelay apparatuses; and a management computer for managing the pluralityof packet relay apparatuses, wherein the plurality of packet relayapparatuses include first packet relay apparatuses, second packet relayapparatuses, and third packet relay apparatuses located downstream ofthe first packet relay apparatuses and the second packet relayapparatuses, wherein each of the third packet relay apparatuses has afirst path coupled to one of the first packet relay apparatuses to sendand receive traffic and a second path coupled to one of the secondpacket relay apparatuses and being in a blocking state, wherein themanagement computer includes: a state information collection unit foracquiring state information on the first to the third packet relayapparatuses; and a power management unit for selecting a candidatepacket relay apparatus to be deactivated satisfying predeterminedconditions based on the state information as a first packet relayapparatus to be deactivated out of the first packet relay apparatuseswhich can be deactivated when using the second path in the blockingstate to transmit the traffic, deactivating the first packet relayapparatus to be deactivated, releasing the second path in the blockingstate between the third packet relay apparatus and the second packetrelay apparatus for the first packet relay apparatus to switch sendingand receiving the traffic to the second path.

Accordingly, this invention achieves reduction in power consumption in anetwork without effect on the traffic in the network by switching a pathcarrying traffic into a path in a blocking state to deactivate anupstream packet relay apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a topology of a network includinga network management terminal and a plurality of packet relayapparatuses according to an embodiment of this invention.

FIG. 2 is a block diagram illustrating a general configuration of apacket relay apparatus according to the embodiment of this invention.

FIG. 3 is a drawing illustrating an example of the configurationinformation in a packet relay apparatus according to the embodiment ofthis invention.

FIG. 4 is a drawing illustrating an example of the state information ina packet relay apparatus according to the embodiment of this invention.

FIG. 5 is a block diagram illustrating a configuration of the networkmanagement terminal according to the embodiment of this invention.

FIG. 6 is a drawing illustrating an example of the state informationdatabase according to the embodiment of this invention.

FIG. 7 is a screen image illustrating an example of the GUI shown on thedisplay device of the network management terminal according to theembodiment of this invention.

FIG. 8 is a sequence diagram illustrating a process flow for the networkmanagement terminal to reduce the power consumption in the network to bemanaged according to the embodiment of this invention.

FIG. 9 is a flowchart illustrating an example of processing of thenetwork management terminal according to the embodiment of thisinvention.

FIG. 10 is a flowchart illustrating an example of processing of thenetwork management terminal according to a modified embodiment of thisinvention.

FIG. 11 is a flowchart illustrating an example of processing of thenetwork management terminal according to another modified embodiment ofthis invention.

FIG. 12 is a flowchart illustrating an example of processing of thenetwork management terminal according to another modified embodiment ofthis invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, an embodiment of this invention is described with referenceto the accompanying drawings.

(A1) Network Topology

FIG. 1 illustrates an embodiment of this invention and is a blockdiagram illustrating a topology of a network including a networkmanagement terminal and a plurality of packet relay apparatuses.

In FIG. 1, data centers 20 a and 20 b providing two sites are coupledvia the Internet 10. In the data centers 20 a and 20 b, Layer 2 networksare provided with packet relay apparatuses 30 a to 30 g and packet relayapparatuses 30 h to 30 n, respectively. The packet relay apparatuses aregenerally denoted by a reference numeral 30. Paths 40 a to 40 h aregenerally denoted by a reference numeral 40 and paths 50 a to 50 f aregenerally denoted by a reference numeral 50.

These networks uses STP (Spanning Tree Protocol); in the case of thedata center 20 a, the packet relay apparatus 30 a is selected as a rootpacket relay apparatus (hereinafter, root bridge) and in the case of thedata center 20 b, the packet relay apparatus 30 h is selected as a rootbridge.

The STP creates a tree network in which the root bridge is the top toavoid a loop in the paths. The paths 40 a to 40 p forming the trees aredenoted by solid lines in FIG. 1 and packets are transmitted onlythrough these paths.

In the case of data center 20 a, the paths 40 a to 40 h form the tree.It should be noted that, in each packet relay apparatus 30, the portcoupled to a path 40 through which upstream packets are transmitted iscalled a root port.

The paths that are not included in the trees are paths 50 a to 50 fdenoted by broken lines in FIG. 1; these paths 50 are physically coupledbut are in a blocking state in which transmission of packets is blocked.In the case of the data center 20 a, the paths 50 a to 50 c are in theblocking state. In each packet relay apparatus 30, the port coupled to apath in the blocking state is called a blocking port.

These networks are managed by a network management terminal (managementcomputer) 80; configuration of the packet relay apparatuses 30 andacquisition of information on the packet relay apparatuses 30 areperformed by this network management terminal 80. The network managementterminal 80 can communicate with each packet relay apparatus 30 in thedata centers 20 a and 20 b via the Internet 10.

In the data centers 20 a and 20 b, a large number of computers andstorage apparatuses are installed in addition to the packet relayapparatuses 30. In FIG. 1, computers 60 a and 60 b are installed to sendand receive information via the networks to perform desired processing.Furthermore, storage apparatuses 70 a and 70 b are installed to storedata via the networks.

The aforementioned apparatuses are each assigned a MAC address and an IPaddress to be located with these addresses in the network.

Hereinafter, described in detail is a method to reduce the powerconsumed by a network without serious effect on the traffic in thenetwork, taking a case of the network constructed in the data center 20a or 20 b as described above.

The network topology, the number of packet relay apparatuses, the numberof computers 60, and the number of storage apparatuses 70 are notlimited to those shown in the example of FIG. 1 but can employ differentconditions as appropriate.

(A2) Configuration of Packet Relay Apparatus

FIG. 2 is a block diagram illustrating a general configuration of apacket relay apparatus 30. The packet relay apparatus 30 includes aplurality of network interface modules 31 a and 31 b, a switching module32, and a control module 33. Hereinafter, the network interface modulesare generally denoted by a reference numeral 31.

The network interface modules 31 include a plurality of packettransmission/reception ports 34 a to 34 d, controllers 35 a and 35 b,and memories 36 a and 36 b. To the packet transmission/reception ports34 a to 34 d, Ethernet cables are physically coupled. Hereinafter, thepacket transmission/reception ports are generally dented by a referencenumeral 34; the controllers are generally denoted by a reference numeral35; and the memories are generally denoted by a reference numeral 36.

The controller 35 in the network interface module 31 analyzes eachpacket received from the packet transmission/reception port 34 toidentify the destination of the packet. If the destination is adifferent apparatus, the controller 35 locates the network interfacemodule 31 and the packet transmission/reception port 34 of thedestination apparatus and transfers the packet to the switching module32.

On the other hand, if the destination of the packet is the sameapparatus including the controller 35, the controller 35 determines thatthe destination of the packet is the control module 33 and transfers thepacket to the switching module 32. The memory 36 functions as a bufferto temporarily store the packet to be sent or received through thepacket transmission/reception port 34.

Upon receipt of a packet, the switching module 32 sends the packet tothe network interface module 31 or the control module 33 in accordancewith the instruction of the controller 35 concerning the packet.

The control module 33 includes a memory 36 c and a CPU 37 a. The memory36 c holds a program for a software processing unit 38 and the CPU 37 aexecutes the program in the memory 36 c to function as the softwareprocessing unit 38.

The software processing unit 38 includes functional units of a packettransmission/reception unit 39, an STP processing unit 41, an LLDP (LinkLayer Discovery Protocol) processing unit 42, a statistics processingunit 43, an operation management unit 44 and data of configurationinformation 45 and state information 46. The packettransmission/reception unit 39 controls over reception of packets sentto the local apparatus and transmission of packets created in thesoftware processing unit 38 to be sent to remote apparatuses.

The STP processing unit 41 controls over transmission and reception ofSTP packets between packet relay apparatuses 30. The STP processing unit41 transmits and receives STP packets to determine the role of the localapparatus in the STP. If the STP processing unit 41 determines that thelocal apparatus is a root bridge, it records the determination in theconfiguration information 45 and functions as a root bridge thereafter.

If the STP processing unit 41 determines that the local apparatus is nota root bridge (hereinafter, a non-root bridge), it records thedetermination in the configuration information 45 and functions as anon-root bridge thereafter. The STP processing unit 41 transmits andreceives STP packets to also determine the STP roles of the packettransmission/reception ports 34 in the local apparatus.

If the local apparatus is a root bridge, the STP processing unit 41determines that all the packet transmission/reception ports 34 aredesignated ports. The STP processing unit 41 records the determinationon all the packet transmission/reception ports 34 in the configurationinformation 45 and makes the packet transmission/reception ports 34function as designated ports thereafter.

If the local apparatus is a non-root bridge, the STP processing unit 41determines that the packet transmission/reception ports 34 coupled tothe path to the root bridge are root ports. The STP processing unit 41records the determination on the root ports in the configurationinformation 45 and makes the packet transmission/reception ports 34function as root ports thereafter. Furthermore, the STP processing unit41 determines that the packet transmission/reception ports 34 which arenot coupled to the path to the root bridge are designated ports. The STPprocessing unit 41 records the determination on the designated ports inthe configuration information 45 and makes the packettransmission/reception ports 34 function as designated ports thereafter.

The STP processing unit 41 determines that the packettransmission/reception ports 34 to cause a loop are blocking ports. TheSTP processing unit 41 records the information on the blocking ports inthe configuration information 45 and makes the packettransmission/reception ports 34 function as blocking ports thereafter.

The LLDP processing unit 42 controls over transmission and reception ofLLDP packets between packet relay apparatuses 30. The LLDP processingunit 42 transmits and receives LLDP packets to recognize the apparatuses(neighboring nodes) coupled to the packet transmission/reception ports34 of the local apparatus. The LLDP processing unit 42 that recognizesneighboring nodes coupled from the packet transmission/reception ports34 records information on the neighboring nodes in the state information46.

The statistics processing unit 43 measures and manages various numericalvalues in the packet relay apparatus 30. For example, it monitorstransmitted traffic volume and received traffic volume at each packettransmission/reception port 34 to record statistical information in thestate information 46. The statistics processing unit 43 counts thesessions maintained in the packet relay apparatus 30 to record it in thestate information 46. The statistics processing unit 43 also counts theflows being processed in the packet relay apparatus 30 to record it inthe state information 46. The statistics processing unit 43 measures thetraffic volumes, the number of sessions, and the number of flows atpredetermined intervals or in response to a request from an external torecord them in the state information 46 as statistics information.

The operation management unit 44 sets configuration of the packet relayapparatus 30 based on a configuration request sent from the networkmanagement terminal 80. The operation management unit 44 records detailsof the configuration in the configuration information 45. Theconfiguration request includes, for example, a request to start STPoperation and a request to stop STP operation. The operation managementunit 44 also acquires requested information from the state information46 based on a state information reference request sent from the networkmanagement terminal 80. The operation management unit 44 returns theinformation acquired from the state information 46 to the networkmanagement terminal 80. The state information reference request from thenetwork management terminal 80 requests, for example, the STP role ofthe packet relay apparatus 30 determined to enable the STP.

The configuration information 45 stores configuration information on thepacket relay apparatus 30. FIG. 3 is a drawing illustrating an exampleof the configuration information 45 in a packet relay apparatus 30. Theconfiguration information 45 includes functions 451 in the packet relayapparatus 30, parameters 452, and values 453 set to the parameters 452.For example, the line 101 in FIG. 3 indicates that the STP in thefunction 451 is working at a value 453=ON for the parameter 452=RUN.

The state information 46 stores information on states of the packetrelay apparatus 30. FIG. 4 is a drawing illustrating an example of thestate information 46 in a packet relay apparatus 30. The stateinformation 46 includes functions 461 of the packet relay apparatus 30,parameters 462, and values 463 set to the parameters 462. For example,the line 201 in FIG. 4 indicates that, in the function 461=STP, theparameter 462 “role of apparatus” is determined to be the value 463“non-root bridge”. The lines 202 to 204 indicate that, in the function461=STP, the parameter 462=roles of ports are port e=root port, porte2=designated port, and e3=blocking port. The lines 205 to 207 indicatethat, in the function 461=LLDP, the parameter 462=neighboring nodes ofports are the packet relay apparatus 30 b coupled to the port e1, thecomputer 60 a coupled to the port e2, and the packet relay apparatus 30b coupled to the port e3. The same applies to the statistics on the line208 and the subsequent lines, which store values about the CPU usage andthe traffic volumes.

(A3) Configuration of Network Management Terminal

FIG. 5 is a block diagram illustrating a configuration of the networkmanagement terminal 80. The network management terminal 80 is made up ofa general-purpose computer and includes a packet transmission/receptionport 34 e, a hard disk 81, a memory 36 d, and a CPU 37 b. The hard disk81 holds a program for a software processing unit 82 and the CPU 37 bexecutes the program for the software processing unit 82 to function asa packet transmission/reception unit 83 and a network management unit84.

The packet transmission/reception unit 83 controls over transmission andreception of packets through the packet transmission/reception port 34e.

The network management unit 84 is an application for functioning as afrontend to manage packet relay apparatuses 30 and includes a packetrelay apparatus configuration/state information reference unit 85, apower-saving management unit 86, a state information database 87, and auser interface unit 88.

The packet relay apparatus configuration/state information referenceunit 85 creates configuration/state information reference requestmessages in accordance with requests of the power-saving management unit86 and sends them to packet relay apparatuses 30. A configurationrequest message requests, for example, shut-down of the packet relayapparatus 30. A state information reference request message requests,for example, the STP role of the packet relay apparatus 30.

The power-saving management unit 86 stores results obtained from thepacket relay apparatus configuration/state information reference unit 85in the state information database 87. The state information database 87holds the state information 46 on each packet relay apparatus 30, forall of the packet relay apparatuses 30 to be managed by the networkmanagement terminal 80. FIG. 6 is a drawing illustrating an example ofthe state information database 87. The state information database 87includes packet relay apparatuses 871 for storing identifiers (uniquevalues) of packet relay apparatuses 30, functions 872 of the packetrelay apparatuses 30, parameters 873, and values 874 set to theparameters 873. For example, FIG. 6 stores CPU usages, traffic volumes(transmission traffic volumes and reception traffic volumes), the numberof sessions, and the number of flows for all the packet relayapparatuses 30. The network management terminal 80 uses the informationstored in this state information database 87 to create a network thatconsumes less power. The creating a network will be described later.

The user interface unit 88 shows a GUI (Graphical User Interface) tomanage packet relay apparatuses 30 on a display device 89 to receivevarious instructions of the network administrator through a keyboard 90or a mouse 91 operated by the network administrator.

FIG. 7 is a screen image illustrating an example of the GUI shown on thedisplay device 89 of the network management terminal 80. In the pane 701in the middle of the GUI, the topology of the network to be managed bythe network management terminal 80 is depicted with icons representingpacket relay apparatuses 30 and Ethernet cables. This drawing teachesthe network administrator the current network topology. The example ofFIG. 7 shows the topology of the network in the data center 20 a.

In FIG. 7, the paths forming a tree are denoted by solid lines and thepaths coupling blocking ports are denoted by broken lines. The referencesigns a1 to g2 in the drawing represent ports of the packet relayapparatuses 30 a to 30 g. It should be noted that the network to whichthis invention is applied includes a plurality of packet relayapparatuses 30 on the first level each coupled to the root bridge withits root port and a plurality of packet relay apparatuses 30 on thesecond level each coupled to the first level with both of its root portand a blocking port.

In FIG. 7 (FIG. 1), the packet relay apparatuses 30 b, 30 c and 30 dconstitute the first level; the root ports b1, c1, and d1 are coupled tothe root bridge of the packet relay apparatus 30 a.

The packet relay apparatuses 30 e, 30 f, and 30 g constitute the secondlevel and the root ports e1, f1, g1 are coupled to the designated portsb2, c2, and d2 of the packet relay apparatuses 30 on the first level.The packet relay apparatus 30 e is disposed downstream of the packetrelay apparatus 30 b, the packet relay apparatus 30 f is disposeddownstream of the packet relay apparatus 30 c, and the packet relayapparatus 30 g is disposed downstream of the packet relay apparatus 30d, to form the first level and the second level. The blocking ports ofthe second level and the blocking ports of the first level are coupledas shown by the broken lines in the drawing. That is to say, theblocking port e3 of the packet relay apparatus 30 e on the second levelis coupled to the blocking port c3 of the packet relay apparatus 30 c onthe first level, the blocking port f3 of the packet relay apparatus 30 fon the second level is coupled to the blocking port d3 of the packetrelay apparatus 30 d on the first level, and the blocking port g3 of thepacket relay apparatus 30 g on the second level is coupled to theblocking port b3 of the packet relay apparatus 30 b on the first level.

The designated ports of the packet relay apparatuses 30 e, 30 f, and 30g on the second level are coupled to other nodes such as the computer60, as shown in FIG. 1.

As described above, the packet relay apparatuses 30 on the first level,which are downstream of the root bridge, are coupled to the root bridgewith the root ports. The packet relay apparatuses 30 on the second levelare coupled to upstream packet relay apparatuses 30 on the first levelwith the root ports and blocking ports, where the root port and theblocking port of each packet relay apparatus 30 on the second level arecoupled to different packet relay apparatuses 30 on the first level. Asto the path 50 coupling blocking ports shown in FIG. 1, it issatisfactory if at least either the port on the first level or the porton the second level is in the blocking state.

(A4) Procedure to Reduce Power Consumption in Network

FIG. 8 is a sequence diagram illustrating a process flow for the networkmanagement terminal 80 to reduce the power consumption in the network tobe managed. In each packet relay apparatus 30, an STP processing unit 41and an LLDP processing unit 42 are working and hold the STP role of thepacket relay apparatus 30, the STP roles of the packettransmission/reception ports 34, neighboring nodes of the packettransmission/reception ports 34, and the like as the state information46. Furthermore, a statistics processing unit 43 is working in thepacket relay apparatus 30 and holds CPU usage, traffic volume at eachpacket transmission/reception port 34, and the like as the stateinformation 46.

The power-saving management unit 86 in the network management terminal80 periodically, for example once per hour, accesses all of the packetrelay apparatuses 30 to be managed (or the packet relay apparatuses 30in a designated data center) to request them to refer to the STPinformation, LLDP information, and statistics information (Step S401).

Each packet relay apparatus 30 receives the request at the operationmanagement unit 44. The operation management unit 44 acquires requestedinformation from the state information 46 to respond to the networkmanagement terminal 80 (Step S402).

Upon receipt of the information, the power-saving management unit 86 inthe network management terminal 80 saves the acquired information in thestate information database 87. Upon completion of receiving theinformation from all the packet relay apparatuses 30 to be managed andsaving it in the state information database 87, the power-savingmanagement unit 86 in the network management terminal 80 calculates thenetwork topology to extract a packet relay apparatus 30 that can bedeactivated as shown in the flowchart of FIG. 9 (Step S403).

FIG. 9 is a flowchart illustrating an example of processing of thenetwork management terminal 80.

In FIG. 9, the network management terminal 80 first accesses the stateinformation database 87 (501) to determine the packet relay apparatus 30having the lowest CPU usage (502). In the case of the state informationdatabase 87 of FIG. 6, the packet relay apparatus 30 having the lowestCPU usage is the packet relay apparatus 30 b. It can be considered thatthis packet relay apparatus 30 b will less affect the traffic in thenetwork if it is deactivated because its CPU usage is lowest.Accordingly, the power-saving management unit 86 selects this packetrelay apparatus 30 b as a candidate to be deactivated (packet relayapparatus A).

Next, the power-saving management unit 86 in the network managementterminal 80 refers to the state information database 87 to locatedesignated ports of the packet relay apparatus 30 b (503). In the caseof the state information database 87 of FIG. 6, the designated port ofthe packet relay apparatus 30 b is the packet transmission/receptionport b2. Inversely, the neighboring node (first neighboring node)coupled from the designated port b2 uses its port for this path as aroot port and sends traffic to the root bridge via this path.Accordingly, to investigate the effect on the traffic using thedesignated port b2, the power-saving management unit 86 in the networkmanagement terminal 80 refers to the state information database 87 tolocate the first neighboring node (neighboring node B in FIG. 9) coupledto the designated port b2 (504).

In the case of the state information database 87 of FIG. 6, the firstneighboring node of the packet transmission/reception port b2 of thedesignated port is the packet relay apparatus 30 e (lines 303 and 306).The packet relay apparatus 30 e uses this path to send traffic to theroot bridge.

Next, the power-saving management unit 86 in the network managementterminal 80 refers to the state information database 87 to determinewhether the packet relay apparatus 30 e of the first neighboring nodehas a blocking port and if it has a blocking port, it locates theblocking port of the first neighboring node (505).

The power-saving management unit 86 further refers to the stateinformation database 87 to locate the neighboring node (secondneighboring node) coupled from the blocking port of the firstneighboring node (506). In the case of the state information database 87of FIG. 6, the packet relay apparatus 30 e has a blocking port e3 (line321) and the second neighboring node (neighboring node C in FIG. 9)coupled from the port e3 is the packet relay apparatus 30 c (line 322).

Next, the power-saving management unit 86 refers to the stateinformation database 87 to locate the third neighboring node(neighboring node D in FIG. 9) coupled from the root port of the packetrelay apparatus 30 c and determines whether the third neighboring nodeis the root bridge coupled from the root port of the second neighboringnode (507). In the example of FIG. 1, the third neighboring node coupledfrom the root port of the packet relay apparatus 30 c is the packetrelay apparatus 30 a, which functions as a root bridge. This means thatthe packet relay apparatus 30 e has a path coupled to the root bridgebeyond the blocking port. In this case, the packet relay apparatus 30 e,which is coupled downstream (from the designated port b2) of the packetrelay apparatus 30 b having the lowest CPU usage, can access the rootbridge of the third packet relay apparatus 30 a from the blocking porte3 via the second packet relay apparatus 30 c; accordingly, thepower-saving management unit 86 proceeds to the next Step 509. As to theterms of upstream and downstream of a packet relay apparatus 30 in adata center 20, the direction toward the root bridge is defined asupstream and the direction toward the leaves where the computer 60 orthe storage apparatus 70 are coupled is defined as downstream.

If the neighboring node cannot access the root bridge from the blockingport, the power-saving management unit 86 proceeds to Step 508. Thepower-saving management unit 86 determines whether the third neighboringnode coupled from the root port of the second neighboring node is thepacket relay apparatus A, which is the candidate to be deactivated(508). If the neighboring node is the packet relay apparatus of thecandidate to be deactivated (YES at 508), the power-saving managementunit 86 proceeds to Step 512 to update the state information database87, and returns to Step 501 to repeat the foregoing processing until anew candidate to be deactivated appears.

If the neighboring node is not a candidate to be deactivated and thereis no path coupled to the root bridge beyond the blocking port, thepower-saving management unit 86 proceeds to Step 511 to determine thatthere is no packet relay apparatus 30 for the candidate to bedeactivated and terminates the processing.

Through the foregoing processing, the power-saving management unit 86has determined whether a packet relay apparatus 30 located downstream ofthe packet relay apparatus 30 having a low CPU usage can access the rootbridge if it sends traffic from a blocking port (507). The power-savingmanagement unit 86 which has determined that the root bridge isreachable next determines whether the bandwidth of the path using theblocking port of the foregoing downstream packet relay apparatus mightcause overflow when the current traffic flowing through the root port isswitched to the blocking port (509).

In the case of this embodiment, the power-saving management unit 86compares the traffic volume at the root port e1 of the packet relayapparatus 30 e located downstream of the candidate to be deactivatedwith the bandwidth of the blocking port e3 coupled to the packet relayapparatus 30 c and if it determines that bandwidth overflow will notoccur, it proceeds to Step 510.

If the traffic volume at the root port e1 of the packet relay apparatus30 e exceeds the bandwidth of the blocking port e3 coupled to the packetrelay apparatus 30 c, overflow will occur. The power-saving managementunit 86 proceeds to Step 512 to update the state information database87, and repeats the foregoing processing.

At Step 510, the power-saving management unit 86 selects the candidateto be deactivated, the packet relay apparatus 30 b having a low CPUusage, as the packet relay apparatus to be deactivated. Then, thepower-saving management unit 86 changes the blocking port of the packetrelay apparatus 30 e, which is located downstream of the packet relayapparatus 30 b to be deactivated, into a root port.

Next, at Step S404 in FIG. 8, the power-saving management unit 86requests for deactivation of the packet relay apparatus 30 b having thelow CPU usage selected to be deactivated. In this embodiment, thepower-saving management unit 86 sends an instruction to change theblocking port e3 of the packet relay apparatus 30 e to a root port anddeactivate the packet relay apparatus 30 b.

When the power-saving management unit 86 in the network managementterminal 80 receives a response to the instruction for deactivation fromthe packet relay apparatus 30 b (S405), it updates the informationconcerning STP and LLDP in the state information database 87 andterminates the processing.

Repeating the foregoing processing to release a path in a blocking stateenables deactivation of a packet relay apparatus 30 wasting power in thenetwork, which reduces the power consumption in the network. Theforegoing processing under a network environment where STP isfunctioning can prevent generation of a loop, while reducing the powerconsumption in the network without serious effect on the traffic flow inthe network.

The above-described embodiment provided an example that the power-savingmanagement unit 86 returns to Step 501 after updating the stateinformation database 87 if the packet relay apparatus 30 e locateddownstream the candidate to be deactivated, the packet relay apparatus30 b, cannot access the root bridge of the third packet relay apparatus30 a from the blocking port e3, or if the bandwidth of this path causesoverflow. However, the processing is not limited to this. For example,if the packet relay apparatus 30 e located downstream of the candidateto be deactivated cannot access the root bridge from the blocking porte3, the power-saving management unit 86 may terminate the processing andrestart the processing of FIGS. 8 and 9 after a certain time period.

The above-described example of FIG. 9 provided an example that refers tothe CPU usages of the packet relay apparatuses 30 to select a candidateto be deactivated; however, the procedure is not limited to this. Acandidate packet relay apparatus 30 to be deactivated may be selectedbased on the traffic volume, the number of sessions, or the number offlows.

In the case of referring to the traffic volume, the power-savingmanagement unit 86 locates the packet relay apparatus 30 having theleast total traffic volume (the sum of the transmission traffic volumeand the reception traffic volume) with reference to the stateinformation database 87 to determine it to be the candidate to bedeactivated. That is to say, Step 502 in FIG. 9 should be changed toselecting a packet relay apparatus 30 having the least total trafficvolume as a candidate to be deactivated, as illustrated in Step 502A inFIG. 10.

In the case of referring to the number of sessions, the power-savingmanagement unit 86 locates the packet relay apparatus 30 having thesmallest number of sessions with reference to the state informationdatabase 87 to determine it to be the candidate to be deactivated. Thatis to say, Step 502 in FIG. 9 should be changed to selecting a packetrelay apparatus 30 having the fewest sessions as a candidate to bedeactivated, as illustrated in Step 502B in FIG. 11.

In the case of referring to the number of flows, the power-savingmanagement unit 86 locates the packet relay apparatus 30 having thesmallest number of flows with reference to the state informationdatabase 87 to determine it to be the candidate to be deactivated. Thatis to say, Step 502 in FIG. 9 should be changed to selecting a packetrelay apparatus 30 having the fewest flows as a candidate to bedeactivated, as illustrated in Step 502C in FIG. 12.

This invention can be configured as a network management method or acomputer program to be executed in a network management terminal, inaddition to the above-described system including the packet relayapparatuses 30 and the network management terminal 80. The computerprogram may be stored in a computer-readable storage medium. Examples ofthe storage medium include various media: a floppy disk, a CD-ROM, aDVD-ROM, a magnetic optical disc, a memory card, and a hard disk.

Embodiments of this invention have now been described. However, thisinvention is not limited to the embodiments described above, and itwould be easy for those skilled in the art to modify, add, or convertelements of the embodiments described above within the scope of thisinvention. For instance, a system or an apparatus to which thisinvention is applied can have only a part of the configurations of theplurality of embodiments described above, or can include all componentsof the plurality of embodiments described above. This invention allowsfor substituting some elements of the configuration of one embodimentwith elements of another embodiment, and allows for adding a part of theconfiguration of one embodiment to another embodiment.

What is claimed is:
 1. A network management system comprising: a networkincluding a plurality of packet relay apparatuses; and a managementcomputer for managing the plurality of packet relay apparatuses, whereinthe plurality of packet relay apparatuses include first packet relayapparatuses, second packet relay apparatuses, and third packet relayapparatuses located downstream of the first packet relay apparatuses andthe second packet relay apparatuses, wherein each of the third packetrelay apparatuses has a first path coupled to one of the first packetrelay apparatuses to send and receive traffic and a second path coupledto one of the second packet relay apparatuses and being in a blockingstate, wherein the management computer includes: a state informationcollection unit for acquiring state information on the first to thethird packet relay apparatuses; and a power management unit forselecting a candidate packet relay apparatus to be deactivatedsatisfying predetermined conditions based on the state information as afirst packet relay apparatus to be deactivated out of the first packetrelay apparatuses which can be deactivated when using the second path inthe blocking state to transmit the traffic, deactivating the firstpacket relay apparatus to be deactivated, releasing the second path inthe blocking state between the third packet relay apparatus and thesecond packet relay apparatus for the first packet relay apparatus toswitch sending and receiving the traffic to the second path.
 2. Thenetwork management system according to claim 1, wherein the networkcouples the second packet relay apparatuses and the third packet relayapparatuses via blocking ports based on Spanning Tree Protocol, andwherein the power management unit releases blocking ports of the thirdpacket relay apparatus and the second packet relay apparatus for thefirst relay apparatus to switch sending and receiving the traffic to thesecond path.
 3. The network management system according to claim 2,wherein each of the first to the third packet relay apparatuses includesa CPU for computing, and a statistics processing unit for acquiring aCPU usage and a traffic volume, wherein the state information collectionunit acquires the CPU usages and the traffic volumes of the first to thethird packet relay apparatuses as state information, and wherein thepower management unit selects the candidate packet relay apparatus to bedeactivated as the packet relay apparatus to be deactivated in a casewhere the candidate packet relay apparatus is a first packet relayapparatus having a lowest CPU usage among the first packet relayapparatuses and the second packet relay apparatus for the candidatefirst packet relay apparatus is able to carry the traffic volume of thecandidate first packet relay apparatus.
 4. The network management systemaccording to claim 2, wherein each of the first to the third packetrelay apparatuses includes a statistics processing unit for acquiring atraffic volume, wherein the state information collection unit acquiresthe traffic volumes of the first to the third packet relay apparatusesas state information, and wherein the power management unit selects thecandidate packet relay apparatus to be deactivated as the packet relayapparatus to be deactivated in a case where the candidate packet relayapparatus is a first packet relay apparatus having a least trafficvolume among the first packet relay apparatuses and the second packetrelay apparatus for the candidate first packet relay apparatus is ableto carry the traffic volume of the candidate first packet relayapparatus.
 5. The network management system according to claim 2,wherein each of the first to the third packet relay apparatuses includesa statistics processing unit for acquiring the number of sessions and atraffic volume, wherein the state information collection unit acquiresthe numbers of sessions and the traffic volumes of the first to thethird packet relay apparatuses as state information, and wherein thepower management unit selects the candidate packet relay apparatus to bedeactivated as the packet relay apparatus to be deactivated in a casewhere the candidate packet relay apparatus is a first packet relayapparatus having a smallest number of sessions among the first packetrelay apparatuses and the second packet relay apparatus for thecandidate first packet relay apparatus is able to carry the trafficvolume of the candidate first packet relay apparatus.
 6. The networkmanagement system according to claim 2, wherein each of the first to thethird packet relay apparatuses includes a statistics processing unit foracquiring the number of flows and a traffic volume, wherein the stateinformation collection unit acquires the numbers of flows and thetraffic volumes of the first to the third packet relay apparatuses asstate information, and wherein the power management unit selects thecandidate packet relay apparatus to be deactivated as the packet relayapparatus to be deactivated in a case where the candidate packet relayapparatus is a first packet relay apparatus having a smallest number offlows among the first packet relay apparatuses and the second packetrelay apparatus for the candidate first packet relay apparatus is ableto carry the traffic volume of the candidate first packet relayapparatus.
 7. A network management computer for managing a networkincluding a plurality of packet relay apparatuses, the managementcomputer comprising: a packet relay apparatus configuration unit formanaging the plurality of packet relay apparatuses including firstpacket relay apparatuses, second packet relay apparatuses, and thirdpacket relay apparatuses located downstream of the first packet relayapparatuses and the second packet relay apparatuses, each of the thirdpacket relay apparatuses having a first path coupled to one of the firstpacket relay apparatuses to send and receive traffic and a second pathcoupled to one of the second packet relay apparatuses and being in ablocking state, a state information collection unit for acquiring stateinformation on the first to the third packet relay apparatuses; and apower management unit for selecting a candidate packet relay apparatusto be deactivated satisfying predetermined conditions based on the stateinformation as a first packet relay apparatus to be deactivated out ofthe first packet relay apparatuses which can be deactivated when usingthe second path in the blocking state to transmit the traffic,deactivating the first packet relay apparatus to be deactivated,releasing the second path in the blocking state between the third packetrelay apparatus and the second packet relay apparatus for the firstpacket relay apparatus to switch sending and receiving the traffic tothe second path.
 8. The network management computer according to claim7, wherein the network couples the second packet relay apparatuses andthe third packet relay apparatuses via blocking ports based on SpanningTree Protocol, and wherein the power management unit releases blockingports of the third packet relay apparatus and the second packet relayapparatus for the first relay apparatus to switch sending and receivingthe traffic to the second path.
 9. The network management computeraccording to claim 8, wherein the state information collection unitacquires CPU usages and traffic volumes of the first to the third packetrelay apparatuses as state information, and wherein the power managementunit selects the candidate packet relay apparatus to be deactivated asthe packet relay apparatus to be deactivated in a case where thecandidate packet relay apparatus is a first packet relay apparatushaving a lowest CPU usage among the first packet relay apparatuses andthe second packet relay apparatus for the candidate first packet relayapparatus is able to carry the traffic volume of the candidate firstpacket relay apparatus.
 10. The network management computer according toclaim 8, wherein the state information collection unit acquires trafficvolumes of the first to the third packet relay apparatuses as stateinformation, and wherein the power management unit selects the candidatepacket relay apparatus to be deactivated as the packet relay apparatusto be deactivated in a case where the candidate packet relay apparatusis a first packet relay apparatus having a least traffic volume amongthe first packet relay apparatuses and the second packet relay apparatusfor the candidate first packet relay apparatus is able to carry thetraffic volume of the candidate first packet relay apparatus.
 11. Thenetwork management computer according to claim 8, wherein the stateinformation collection unit acquires the numbers of sessions and trafficvolumes of the first to the third packet relay apparatuses as stateinformation, and wherein the power management unit selects the candidatepacket relay apparatus to be deactivated as the packet relay apparatusto be deactivated in a case where the candidate packet relay apparatusis a first packet relay apparatus having a smallest number of sessionsamong the first packet relay apparatuses and the second packet relayapparatus for the candidate first packet relay apparatus is able tocarry the traffic volume of the candidate first packet relay apparatus.12. The network management computer according to claim 8, wherein thestate information collection unit acquires the numbers of flows andtraffic volumes of the first to the third packet relay apparatuses asstate information, and wherein the power management unit selects thecandidate packet relay apparatus to be deactivated as the packet relayapparatus to be deactivated in a case where the candidate packet relayapparatus is a first packet relay apparatus having a smallest number offlows among the first packet relay apparatuses and the second packetrelay apparatus for the candidate first packet relay apparatus is ableto carry the traffic volume of the candidate first packet relayapparatus.
 13. A network management method of managing a networkincluding a plurality of packet relay apparatuses with a managementcomputer, the plurality of packet relay apparatuses including firstpacket relay apparatuses, second packet relay apparatuses, and thirdpacket relay apparatuses located downstream of the first packet relayapparatuses and the second packet relay apparatuses, each of the thirdpacket relay apparatuses having a first path coupled to one of the firstpacket relay apparatuses to send and receive traffic and a second pathcoupled to one of the second packet relay apparatuses and being in ablocking state, the management method comprising the steps of: a firststep of acquiring state information on the first to the third packetrelay apparatuses; a second step of selecting a candidate packet relayapparatus to be deactivated satisfying predetermined conditions based onthe state information as a first packet relay apparatus to bedeactivated out of the first packet relay apparatuses which can bedeactivated when using the second path in the blocking state to transmitthe traffic; a third step of deactivating the first packet relayapparatus to be deactivated; and a fourth step of releasing the secondpath in the blocking state between the third packet relay apparatus andthe second packet relay apparatus for the first packet relay apparatusto switch sending and receiving the traffic to the second path.
 14. Thenetwork management method according to claim 13, wherein the networkcouples the second packet relay apparatuses and the third packet relayapparatuses via blocking ports based on Spanning Tree Protocol, andwherein the fourth step releases blocking ports of the third packetrelay apparatus and the second packet relay apparatus for the firstrelay apparatus to switch sending and receiving the traffic to thesecond path.